Serological and RT-PCR evaluation of African yam bean (Sphenostylis stenocarpa (Hochst ex. A. Rich) Harms) accessions to viral resistance under field condition.

African yam bean (AYB) (Sphenostylis stenocarpa (Hochst ex. A. Rich.) harms) an underutilized legume that produces nutritionally healthy seeds and tubers in some variety. The low yield of the crop is attributed to production constraints such as attacks by pest and disease-causing organisms such as fungi, bacteria and viruses. In this study, one hundred AYB accessions were evaluated for resistance to viral infection. The AYB accessions were planted using a randomized complete block design on the experimental field at the International Institute of Tropical Agriculture (IITA) Ibadan, Nigeria. Viral disease severity was assessed at 10, 12, 14, 16 and 18 weeks after planting (WAP) based on disease symptoms using disease severity index on visual scale of 1-5. Antigen-coated plate enzyme linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction were used to index diseased leaf samples collected from the field. Result from five virus species (Cowpea mild mottle virus, Cowpea mottle virus, Southern bean mosaic virus, Cowpea mosaic virus and Bean common mosaic virus) were detected in few accessions while mixed infections were observed in some accessions. TSs-552, TSs-577, TSs-580, TSs-560 and TSs-600 were devoid of viruses and could be resistant. There were no significant differences at p < 0.05 in the mean disease incidence (DI) of viral diseases. However, at 18 weeks after planting, TSs-604 had the highest (100%) mean DI while TSs-584 had the lowest (13.33%) mean DI. Cluster analysis based on the AUDPC produced 6 main clusters, the clusters revealed grouping patterns in which AYB lines with similar resistance ratings were shown to form unique clusters. The information generated from this study will contribute to the development of strategies in the management of virus diseases infecting AYB.

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